Folding bleacher and operator therefor



June 18, 1963 R. J. LAPPIN ETAL 3,094,186

FOLDING BLEACHER AND OPERATOR THEREFOR Filed March 28, 1958 S Sheets-Sheet 1 June 18, 1963 R. J. LAPPIN ETAL 3,094,186

FOLDING BLEACHER AND OPERATOR THEREFOR Filed March 28, 1958 3 Sheets-Sheet 2 June 1953 R. J. LAPPIN ETAL 3,094,186

FOLDING BLEACHER AND OPERATOR THEREFOR Filed March 28, 1958 3 Sheets-Sheet 3 I? .INVENTORS,

I 0 o p 1% KM I United States Patent assignors to Brunswick Corporation, a corporation of Delaware Filed Mar. 28, 1958, Ser. No. 724,628 2 Claims. (Cl. 180-19) This invention relates to the art of folding bleachers of the general type disclosed in the Lappin et a1. Patent 2,815,541. Such bleachers commonly include a rear section adapted for attachment to an upstanding wall structure or the like and a number of foldable front sections usually folded and unfolded manually.

It is a general object of this invention to provide a new and improved power operator for folding and unfolding such bleacher structures.

Another object is to provide a tractor type power operator of the character described having an improved drive means which provides a positive synchronized straight-line drive to both propelling wheels of the operator when coupled to a bleacher, and which permits independent differential movement of the wheels when the operator is uncoupled.

A further object is to provide a new and improved power operator of the type described including a pair of propelling wheels, a large driven sprocket on each wheel, a double chain on each sprocket with one strand of the chain enmeshed with the sprocket teeth and an adjacent strand free, a drive motor having a double ended drive shaft provided with a small drive sprocket on each end, and means mounting the motor for bodily movement to position the drive sprockets in and out of mesh with the free chain strands.

Another object is to provide a new and improved power operator unit of the type described including a reversible drive motor which enables forward or reverse operation of the unit without the need for back gearing or gear change systems.

A further object is to provide a new and improved power operator of the type described including a stand for supporting a person to increase the traction of the propelling wheels on a floor or the like.

It is also an object of the invention to provide a new and improved power operator of the type described including a coupling for connecting the operator to a folding bleacher and means for breaking the bleacher linkage preparatory to folding as the coupling is connected to the bleacher.

Another object is to provide a new and improved power operable folding bleacher construction including means engageable by a power operator coupling to break the bleacher linkage preparatory to folding as the coupling is connected to the bleacher.

A further object is to provide a new and improved fold ing bleacher construction including means for locking the front two bleacher sections together in folded condition to enable connection of a power operator thereto in cramped quarters.

Other objects and advantages will become readily apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevational view, partly broken away, of a power operator unit embodying the principles of the present invention;

FIG. la is a fragmentary side elevational view, similar to FIG. 1, showing a lock plug in operative position.

FIG. 2 is a plan View of the operator unit illustrated in FIG. 1, in section at about the line 2-2 of FIG. 1, and partly broken away.

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FIG. 3 is a fragmentary plan view taken at about the line 3-3 of FIG. 1;

FIG. 4 is a rear elevational view of the power operator unit illustrated in FIGS. 1 and 2, partly in section;

FIG. 5 is an enlarged fragmentary sectional View at about the line 5-5 of FIG. 3;

FIG. 6 is a fragmentary sectional view at about the line 6-6 of FIG. 5;

FIG. 7 is a fragmentary end elevational view, partly broken away, of a power operable folding bleacher adapted for use with the power operator unit illustrated in the preceding figures, illustrating the bleacher in extended or unfolded condition;

FIG. 8 is a fragmentary plan view of the bleacher structure illustrated in FIG. 7;

FIG. 9 is an end elevational view of a bleacher structure similar to that of FIGS. 7 and 8, in folded condition, and including a modification of the bleacher structure;

FIG. 10 is a fragmentary sectional view taken at about the line 10-10 of FIG. 9; and

FIG. 11 is a fragmentary side elevational view showing another bleacher modification.

While illustrative embodiments of the invention are shown in the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms, and it should be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and are not intended to limit the invention to the embodiments illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings in more detail, the power operator unit of this invention includes I8. generally horizontally disposed U-shaped frame member 10 which includes parallel horizontal legs 11 each including a its length, has a laterally outwardly projecting stub shaft or axle 16 suitably secured thereto as by welding for sup porting propelling wheels for the unit. The propelling wheels are supported on the axles 16 through the medium of suitable bearing means 117 and each includes a central hollow hub portion 18 rotatable on the axle, an outwardly extending annular web portion 119 suitably secured to the hub, a rim 20 at the periphery of the web for supporting a suitable tire 21, and a hub cap 22. In this manner, the propelling wheels are independently rotatable on the frame structure for differential movement when the drive is disengaged and thereby enable manipulation of the unit by hand. 7

The center of gravity of the unit is located approximately over the common axis of the propelling wheels, and the Weight at opposite ends of the unit from the wheel axis is approximately balanced to facilitate manual handling when the unit is not coupled to -a bleacher so that an operating person need only balance the unit while the wheels support most of the weight. However, the right end of the unit from the wheel axis, as viewed in FIGS. 1 and 2, is slightly heavier than the left end to enable parking when the unit is not in use, and to stabilize the unit for this purpose a third wheel 23 is rotatable in a forked wheel support :24 secured to a bracket 25 extending between and secured to the frame legs 1-1.

To facilitate manipulation of the unit manually, suitable handle means are provided including two handles 27 each including lower upright end portion 28 secured to a frame leg 11, an intermediate rearwardly slanting portion 29 and an upper end hand grip portion 30. The slanting portions of the handles are reinforced by two braces each including a lower end portion 32 secured to a frame leg 11, an upright intermediate portion 33, and an upper rearwardly slanting end portion 34 disposed along the inside of and secured to the adjacent slanting intermediate portion 29 of handle 27. The upper end portions 34 are joined by a transverse connecting member 35. The slanting portions 34 of the braces are welded or otherwise secured to the intermediate portions 29 of the handles. The portions 34 and 35 of the braces and the adjacent portions of the handles form a mount for supporting a plate 37 which is utilized as a control panel.

Power is supplied to the propelling wheels through the medium of large sprockets 39, one secured to the hub portion 18 of each propelling wheel. Each sprocket 39 has a double chain thereon including a first chain strand 40 which tightly encircles the sprocket 39 completely, meshing with all of the sprocket teeth, and a second inwardly disposed chain strand 41 parallel to and secured to the first chain strand, The second chain strand is entirely free, and functions as, an internal ring gear, being adapted to receive a relatively small drive sprocket 42 movable into and out of meshing engagement therewith. The drive sprockets 42 are disposed within the periphery of the chain strands 41 and form a part of a drive, unit to be described.

The power drive unit for supplying power to the propelling wheels comprises a motor support in the form of a Ushaped bracket pivoted on the frame and including an upright connecting web portion 45 having parallel forwardly extending leg portions 46 pivoted at their ends respectively on legs 11 as at 47. The central web portion 45 has a base 49 of a motor drive unit 50 secured thereon as by bolts 51. When the pivoted bracket and the motor drive unit are allowed to pivot downwardly about the pivot axis 47 to the position shown, the weight of the motor drive unit is supported by means of a cross rod 52 passing through the bracket legs 46 and having opposite ends 52;; projecting outwardly to rest on the frame legs 11.

T drive m t 0 ha a d ub e ded driv Sh t o P y, co p i e a cl di a d iv mo or a d a s ar r u er av g a doubl n ed dr e sha in lu ing shaft ends 54 each of which carries one. of the relatively small driv sp ocket 42 p eviou y de cr be It will be, understood that the motor drive unit may be pivoted upwardly from the position illustrated to disengage the sprockets 42 from the chain strands 41 and thereby free the propelling wheels tor independent differential rotation to facilitate manipulation of; the manually when it is, not coupled to a bleacher. When the motor drive unit is pivoted downwardly to the position shown to mesh the drive sprockets 42 with the chain strands 41, a positive synchronous drive is applied to both propelling wheels to produce movement of the entire unit in a straight line path as is important to obtain proper folding and on folding of a foldable bleacher linkage without binding.

Means for pivoting the motor drive unit and its supporting bracket includes a pair of parallel 56 having their forward ends rigidly secured to the bracket legs 46 p tiv ly and in uding h rea nd nw rdlyrned portions 57 whi h are joi ed, a ac r p sit n y rea Wardly nt u 58 Th lug 58'. provi e a pivo al o neotion at 6.0 for the. lower end; of a clutch rod; 61. As best seen in FIG. 5, the upper end of the clutch rod is laterally bent and pivotally connected to a slide rod 63 which. is slidable in a bearing 64 integral with a bracket 65. Bracket 65 is secured as by bolts 66 to a plate 67 Welded or-otherwise suitably secured to the crosspiece 35 of the reinforcing: brace for the handles. The. upper end of the slide rod 63 is. pivoted at 69 to parallel links 70 having their upper ends pivoted at 71 to a manually acces- 4 sible handle 72. The handle 72 has an upwardly projecting lug pivoted at 73 to a portion of the bracket 65.

In operation, it will 'be understood that movement of the handle to the full line position shown allows movement of the slide rod 63 and the clutch rod 61 downwardly to lower the motor drive unit to a position meshing the drive sprockets 42 with the chain strands 41. Conversely, the handle 72 maybe pivoted in a counterclockwise direction about the pivot 73 to the broken line position illustrated in FIG. 5 to thereby elevate the slide rod 63 and the clutch rod 61, raising the motor drive unit and disengaging the drive sprockets 42 from the chain strands 41.

To prevent energization of the drive motor until the drive sprockets 42 are in mesh with chain strands 41, a safety switch 75 is suitably supported beneath the control panel 37. This switch is connected in the motor circuit and is of the normally open type so as to prevent energizetion of the motor until such time as it is closed. The switch includes a button 76 engageable by a switch actuating member 77 on one of the links 70 which is moved to switch closing position when the handle is moved to the full line position shown.

The drive motor is wired through a conductor 80 leading to the control panel which in turn has a rather long conductor '81 terminating in a plug 82 adapted to be positioned in any convenient receptacle providing electrical mwer for energizing the motor. A conductor 83 leads from the control panel to a position adjacent one of the hand grip portions 3 1 where an email switch 84 is conveniently positioned for operation by a person handling the unit. The drive motor is of a conventional reversible type, and the control panel includes a reversing switch 86 for obtaining operation of the motor either forwardly or reversely.

"th use of a reversible motor enables forward or reverse operation of the unit without the need for compli cated and expensive back gearing or gear change systems. The drive train from the motor to the propelling wheels provides a positive synchronized drive when coupled and enables difierential rotation of the propelling wheels when uncoupled, all without the necessity for a transmission including complex dilferential and clutch mechanisms.

At the front end of the frame 10, coupling means is provided for detachably connecting the power operator unit to a bleacher including a pair of coupling members, one secured to each frame leg 11. In a preferred form, each coupling member comprises an upright bracket 90 (FIG. 1) fitted in the slotted end of frame leg 11 and bifurcated at the lower end, as best seen in FIG. 4, to support a roller 91. The rollers 91 facilitate manipulation of the unit when the front end must be lowered to connect the coupling members to a bleacher. The coupling members may be welded or otherwise secured to the frame legs 11, and at the upper ends are each formed with an upwardly opening slot 92 (FIG. l) elongated in a front to rear direction to receive a bleacher tow bar such as that illustrated at 93a and 93b. After the front end of the frame is lowered and moved beneath the bleacher tow bar and then elevated to the. position shown in FIG. 1, the tow bar is abuttable against the coupling member at opposite ends of the slot 92 depending on whether the operator is moved toward or away from the bleacher. In order to unfold the bleacher, the operator unit is moved in a direction away from the. bleacher (to the. right in FIG. 1) to engage the tow bar as at 93a to pull the same outwardly. In order to fold the bleacher, the operator unit is moved in a direction toward the bleacher (toward the left in FIG. '1) to engage the tow bar as at 93b to push the same inwardly.

When the bleacher is extended or unfolded for use, the foldable linkage associated therewith is locked in the sense that more horizontally directed pressure on a tow bar such as that at 93 will not fold the bleacher. In stead, the linkage connecting the first two sections of the bleacher must be unlocked or broken. Normally, this linkage is broken manually to initiate folding. According to the invention, the linkage is broken automatically by cam means provided on the front end of the frame, after which pressure applied by pushing horizontally on the tow bar completes the folding. The cam means comprises the front faces 95 of the lower portions of coupling brackets 90. The cam surfaces 95 are positioned to engage a bleacher linkage trip arm such as that indicated in broken lines at 96 (FIG. 1) when the coupling brackets are positioned to engage the tow bar as at 93a. Thus, movement to the left in FIG. 1 to take up the lost motion in the coupling means enables the cam means to pivot the trip arm in a clockwise direction to break the bleacher linkage before the coupling members engage the tow bar as at 9312 to complete the folding.

While the power drive described above is calculated to rotate the two propelling wheels synchronously to obtain straightline movement of the operator unit in a path normal to the length of a folding bleacher, :during op eration, a number of conditions beyond control may cause the operator unit to deviate from a straightline path. For example, if there occurs only a slight difference in air pressure in the inflatable tires 21, the unit may tend to travel in a wide circle rather than a straightline path. During unfolding particularly, such deviation is undesirable because as the bleacher linkage approaches its extended position, a limited lateral movement is permitted in the linkage because the bleacher is relatively unguided, and any deviation of the unit from a st-raightline path at this time may cause the linkage to bind and become damaged or inoperative. Binding of the linkage is less likely to occur on folding the bleacher as the linkage is guided to a certain extent by the folding, doubling and overlapping of link parts as the bleacher approaches folded position.

Accordingly, in order to insure straightline tracking of the operator unit on unfolding a bleacher, coupling members 90 each include a lock lug 97 pivotable thereon adjacent the rear end of upwardly opening coupling slot 92. Each lock lug is pivoted at 98 on coupling member 90 and movable between a first position (FIGS. 1 and 2) extending rearwardly from pivot 98 and a second position (FIG. 1a) extending forwardly from pivot 98. In the first position, the lugs have no function and are normally so positioned when the operator is not in use or when it is being used for folding. The lock lugs are movable to the second position on coupling the operator to a bleacher for unfolding, and being at spaced positions along the bleacher bar and substantially in engagement with the bar at the front side thereof hold the operator aligned on a path normal to the tow bar. Since the lugs prevent lost motion of the coupling members on the tow bar, the operator is forced to travel in a straightline path thereby insuring proper unfolding of bleacher without binding of the bleacher linkage.

It will be understood that there may be departures from the specific construction shown without departing from the scope of the appended claims. Particularly, changes may be made in the supporting frame structure without altering the function of essential features of the invention.

As previously indicated, the power operator unit described above is intended for use with folding bleacher structures of the general type disclosed in L ppin t a1- 2,8l5,54l. Figs. 7 to 11 in this application illustrate a bleacher construction of the type referred to but not in its entirety. As no claim is made herein to the specific foldable linkage of such bleachers, only a portion of such a structure is shown in order to simplify the drawings. However, suflicient portions of the bleacher are illustrated to enable an understanding of its operation and a clear understanding of the invention of this ap lication.

Referring to FIGS. 7 to 10, bleachers of the character mentioned include a plurality or series of upright sun ports or frames herein illustrated as four, designated A, B, C, and D, seen in end elevation in FIGS. 7 and 9. Frame A is the tallest while frame D is the shortest, frames B and C being stepped downwardly in height from frame A to frame D. Frame A includes two upright tubular members (only one visible) which are secured in laterally spaced relationship by a bracing structure (not visible). Frames B, C, and D include respectively tubular members 101, 102, and 103 each pair of such tubular members being secured in spaced relationship :by a bracing structure similar to that securing the members 100.

Adjacent frames A and B, B and C, and C and D are connected by associated foldable linkage means E, F, and G respectively so as to stack together in closely adjacent parallel relationship, as illustrated in FIG. 9, when the bleacher is not in use. Foldable linkage of the type referred to is provided :at each end of the bleacher, but in order to simplify the drawings only one end of the bleacher is shown and described, it being understood that the other end is identical in structure to the end described.

Upright tubular member 100 of frame A is secured at its lower end to a floor or other supporting surface by any suitable means such as a bracket 105, and at its upper end may be secured to a vertical wall or the like by any suitable means (not illustrated). Tubular members 101 and 102 are movably supported on a floor or the like respectively by rollers 106 and 107, while tubular member 103 is supported by a roller 108 and a U-shaped bracket 109 having a supporting roller 110.

Fixed adjacent the upper ends of members 100, 101,

.and 102 are brackets 112 each of which has an arcuate slot 114. Fixed adjacent the upper end of tubular member 103 is a bracket 113-. Secured to the upper surface of brackets 112 and 113 are seatboards 115 which extend longitudinally for at least the length of frames A, B, C, and D.

Secured to the front of seatboard bracket 113 on tubular member 103 of frame D and extending downwardly therefrom and longitudinally at least the length of frame D is a two section skirtboard including an upper section 138 and a lower section 139 hingedly connected at 140.

Linkage means G foldably interconnecting frames C and D includes two vertically spaced links 116 and 118 each having one end pivotally connected to tubular member 102 and extending forwardly therefrom. Secured to tubular member 103 is a bracket 120 extending upwardly and rearwardly therefrom. A footboard supporting bar 122 is pivotally connected to bracket .120 and, at 124, to the forward end of link 116. A link 126 is pivotally connected at 128 to link 118 and at 130 to bracket 109. Extending vertically between connections 124 and 128 and pivotally mounted therebetween is a vertical link 132. A footboard 133 is secured to footboard supporting bar 122 and extends longitudinally thereon at least the length of frame D.

An arm 134 has one end pivotal-1y connected at 136 to link 1116 and has the other end pivotally connected at 137 to a skirtboard mounting means for frame C.

Movably carried in arcuate slots 114 of brackets 112 on tubular member 100 are a skirtboard bracket and a plate 171, the plate and bracket being connected together at 172 and 173. Pivotally connected at its upper end to bracket 170 and plate 171 is a member having its lower end pivotally connected to the upper end of link 134. Secured to skirtboard bracket 170 and extending longitudinally thereon at least the length of the frame is a skirtboard 177.

Foldable linkage F interconnecting frames B and C includes vertically spaced links 150 and 152, similar to links 116 and 118 in linkage G, each having a rear end (not visible in FIG. 7) pivoted to tubular member 101 and extending forwardly therefrom. Brackets 154 and 156 are secured to tubular member '102 in vertically spaced relation and pivotally carry respectively a rearwardly extending footboard supporting bar 158 and a bell crank member 159. The forward end of link 152 is pivotally connected to the rear end of hell crank member 159 as at 160, and the forward end of link 150 is pivotally connected'to'footboard suppo'nting bar 158 as at 162. Extending vertically between 150 an 152 is a vertical link I64 pivotally connected at its lower end to link 152 and having at its upper end a vertical slot 161 providing a 'slidabl'eand pivotal connection to link 150 at 166.

Fastened to footboard supporting bar 158 and extending longitudinally for at least the length of frame C is a 'footboard 167.

Means are provided for stabilizing the bleacher when unfolded including the bracket 154 on tubular member 102 which has an angled portion 154a operable to support the pivoted footboard supporting bar 158 when it is in a horizontal position to thereby positively prevent further downward movement of the board.

To aid in folding linkage means F, an angled bracket 178 on link 118 is operable upon movement in an up ward direction to engage arm 179 ofbell crank 159 to pivotally move the bell crank 'in a clockwisedirection and break the linkage connection at 160.

A link 134', similar to link 134 in linkage G has its lower endpivotally connected to link 150 at connection 166. Parts completing linkage means F, not visible in FIG. 7, are similar'to those of'the left of vertical link 132 in linkage G. The linkage means E interconnecting frames A and B is similar to the linkage means F.

To ran the bleacher illustrated in FIG. 7 from the 'position shown to the folded position-of FIG. 9, the link connections at 124 and 128 must be broken or unlocked either by raising footb'oard 133 or 'by pulling'skirtboard 1'77 forwardly, or both. Normally, such an operation has been accomplished manually. After this, frame D maybe pushed rearwardly and folding-of the remaining frames and linkage follows automatically.

To unfold the linkage from the position illustrated in FIGJ9 tothat illustratedin FIG. 7,'the front "frame Dis pulled forwardly.

According "totheinvention, in order to facilitate folding of the bleacher "completely by the power'operator unit previously described, the bleacher'of-FIGS. 7 and '8 includes atrip arm'suchas that referred to at 96 in FIG.

'1 engageable by'cam means9 of the power operator unit for breaking the linkage G preparatory to folding the bleacher. The trip arm takes'the form of a member 180 "which is U-shaped'in. plan view as seen in FIG. 8, and

which includes parallel leg portions 181 and a transverse middle leg portion 183. Leg portions 181 are suitably secured to the 'footboard 131i pivoted to frame D as by screws or bolts 185. The member 180 is preferably located centrally of the length of footboard 133, and the forward portions of legs 181 are angled downwardly as "seenat 18-1a-in FIG. 7. The transverse middle leg 18?:

is 'thus disposed-for engagement by the cam surface 95 on coupling members 900i the power operator unit, as illustratedin FIG. 7.

border to facilitate connection ofthe coupling members 90 of the power operator unit to the bleacher, the bleacher includes a tow bar 190 suitably secured to the frame D for receiving the coupling members. As illustrated the tow bar comprises a horizontally disposed tubular rod 190 having opposite end portions supported *res'pectively on upright tubular members 1030f frame D.

The tow bar is attached at each end by means including --a U-bolt 192 onrnember 103- having legs which pass respectively over and'under the tow bar and through plates l9 3 disposed on opposite sides of the tow bar, the U- bolt being secured in place by nuts 194. In this manner, the=tow bar is rigidly attached to the frame D.

In operation, a power operator unit of the type described is moved manually to a position in front of the bleacher where the front end of the frame is lowered, after skirtboard section #139 is elevated, and pushed forwardly to position coupling members beneath the tow bar, after which the front end of the operator unit frame is elevated so that the tow bar is positioned in the :slots '92 of the coupling members. border to properly center the operator unit relative to the bleacher, the tow bar has a centrally disposed guide sleeve I96 thereon which must be embraced at opposite ends by coupling members 90 as illustrated in FIG. 8. As seeniin FIG. 7,=the slots 92 in coupling members 90 allow considerable lost motion of the coupling member on the tow bar. This .permits the coupling members to .be positioned initially on the tow bar as illustrated in :FIG. 7; that is, with the tow bar at the forward end of theslots and with the cam-surface 95 engaging but not pivoting trip arm 181a. As'the power operator unit 'is moved toward the bleacher (to the left in FIG. 7) to take up the lost motion of the coupling member on the tow bar, camsurfaces 95 causes pivoting 'of the'triparm in a clockwise direction to elevate the vertical link 132, breaking the linkage G between frames on link 1-18 engages bell crankarm '17-9 to break linkage F and initiate its folding whichis completed on continued movement of the power operator unit to the left. The

folding of linkage E follows in the same manneras that of linkage -F.

To unfold the bleachencoupling members 90 are connected to the tow bar with the forward ends of slots '92 engaging the tow bar, and lock lugs 97 are moved to the operative positions shown in FIG. la. After this, movement of the :power operator unit to the right unfoldsthe bleacher to the position illustrated in FIG. 7. The positioning of the tow bar at the front end of coupling slots 92, as shown at 93a, permits return of the trip arm to the position of FIG. 7.

FIGS. 9 and 10 illustratea modification ofthe bleacher particularly adapted for use in crowded places. More specifically, where the floorspace in front of a bleacher is limited to a narrow aisle area for example, asby other bleachers or by a railing, there may not be sufiicient space for manipulation of the power operator unit when the bleacheris unfolded. In this case, his sometimes necessary or desirableto manually fold the first'bleacher section including linkage G to position frame D against frame C to thereby provide space for manipulating the power operator unit. In such situations, there is no need'for a trip arm suchas that shownin FIGS. 7 and 8, andthis feature is omit-ted from the bleacher of FIGS. 9 and '10. Instead, meansis-provided for latching frameDto frame C in folded condition to permit use of the operator unit for the remaining .folding and unfolding operation.

Thus, the bleacher of FIGS. 9 and 10 includes a tow bar similar to that in FIGS. 7 and 8 which is attached to frame .D by means similar to that in FIGS. 7 and 8 and designated by primed reference numbers. The latch means comprises a sleeve 200 fitted on the'tow bar 190' atits connection to the upright tubular member 103 of frame D, and embraced by U-bol t 192"and plates 193' as in FIGS. 7 and 8. Thesleeve 200 includes an integral depending leg 201 having a fixedhook 202thereon which embraces tubular member 103 to reinforce the depending leg 201. The leg 201 also has a hook 204 pivoted thereon at 205 and including a'latch portion 204a for embracing upright'tubular member :102-on frame '0 when the frame D is folded against frame 0.

It will be understood that the latch member ZM-posimanually and frame D pushed against frame C to enable latching of hook member 204. On unfolding, after the power opera-tor unit has been utilized to extend the remaining 'bleacher portions, hook 204 is manually disengaged and frame D manually extended from frame C.

In some bleacher installations, it is desirable to omit one or more (depending on length) centrally located sections of seatboards 115 and skirtboards 138--139 and 177, leaving only footboards 133 and 167 which provide stairs for easily ascending or descending the bleacher when unfolded for use. In this event, it will be understood that the elimination of portions of the skirtb'oard 138-139 and the lowest seatbo-ard 115 will leave portions of the tow bar 190 exposed, presenting a hazard likely to trip spectators using the steps provided by footboards. Accordingly, the bleacher modification illustrated in FIG. 11 encompasses a bleacher construction wherein the tow bar is removably mounted to be readily detachable after the bleacher is unfolded to thereby eliminate the trip hazard and to be easily attachable for folding the bleacher where it may remain until the bleacher is again unfolded.

Referring to FIG. 11, wherein like parts are designated by double primed numbers, a tow bar support structure, one provided at each end of the bleacher, includes a pair of half circular clamplike brackets 210 and 2 11 embracing upright tubular member 103" and rigidly secured thereon as by bolts 212 (one visible) on opposing sides of the tubular member. A bracket 214 has upstanding leg portions 215 also secured by bolts 212 and includes a fixed hook 20 (similar to that at 202 in FIGS. 9 and 10) embracing tubular member 103" to reinforce the bracket. A removable hook 204 (similar to that in 204 in FIGS. 9 and 10) is pivoted on bracket 214 at 205" to latch around upright tubular member 102" when the first bleacher frame D is manually folded against the adjacent frame C. Clamplike bracket 211 is formed with an integral forwardly extending tow bar support 2 16 having a downwardly opening recess 217 to receive an upwardly inserted portion of tow bar 190", the latter preferably including a collar 219 fixed thereon to locate the tow bar properly relative to support 216. Adjacent the lower end of recess 217, the support 216 has a detent pin 220 which is preferably of the spring loaded type engageable beneath the tow bar to releasably retain the same in position, permitting insertion and withdrawal of the tow bar from the recess.

We claim:

1. In a power operator for folding bleachers, a frame, a pair of laterally spaced propelling wheels independently rotatable on the frame about a common axis, a handle on the frame for manipulating the operator, a relatively large sprocket secured on each wheel, a double chain on each sprocket including a first strand completely encircling the sprocket tightly for rotation therewith and a second parallel free strand secured to the first adjacent thereto on the side thereof toward the other double chain, a motor support pivoted on the frame between the wheels for movement about an axis parallel to the wheel axis, a drive motor on the motor support having a double ended drive shaft, :a relatively small drive sprocket on each end of the drive shaft positioned respectively within the peripheries of said second strands and engageable therewith, means for pivoting the motor support to mesh the drive sprockets with the second strands to drive the wheels synchronously or to disengage the drive sprockets from the second strands to permit independent differential movement of the wheels, and means for coupling the frame to a folding bieacher.

2. In a power operator for folding bleachers, a frame including a pair of laterally spaced rearwardly extending members, a handle mounted on the frame extending upwardly and rearwardly, a pair of laterally spaced propelling wheels independently rotatable respectively on the frame members on a common axis, each wheel having an internal driven ring gear thereon, a drive unit movably mounted on said frame between said wheels, said drive unit including a reversible drive motor, a double ended drive shaft, and an externally toothed drive gear on each end of the shaft positioned respectively to cooperate with the internal wheel gears, said drive gears movable into an out of positive driving relationship with said internal driven wheel gears when the drive unit is moved between a first position for positive driving and a second position for disengagement of the drive gears to permit independent differential rotation of the wheels, and means for coupling the operator to a folding bleacher.

References Cited in the file of this patent UNITED STATES PATENTS 244,117 Elfers July 12, 1881 2,166,450 Smalley July 18, 1939 2,205,624 Horn June 25, 1940 2,600,720 Abramson June 17, 1952 2,614,642 Dumais Oct. 21, 1952 2,625,230 Burkhardt Jan. 13, 1953 2,665,139 Schroeder Jan. 5, 1954 2,762,443 Dunham Sept. 11, 1956 2,815,541 Lappin et al. Dec. 10, 1957 2,836,253 Lovell May 27, 1958 2,851,179 Vance Sept. 9, 1958 2,968,842 Murphy Ian. 24, 1961 

1. IN A POWER OPERATOR FOR FOLDING BLEACHERS, A FRAME, A PAIR OF LATERALLY SPACED PROPELLING WHEELS INDEPENDENTLY ROTATABLE ON THE FRAME ABOUT A COMMON AXIS, A HANDLE ON THE FRAME FOR MANIPULATING THE OPERATOR, A RELATIVELY LARGE SPROKET SECURED ON EACH WHEEL, A DOUBLE CHAIN ON EACH SPROCKET INCLUDING A FIRST STRAND COMPLETLY ENCIRCLING THE SPROCKET TIGHTLY FOR ROTATION THEREWITH AND A SECOND PARALLEL FREE STRAND SECURED TO THE FIRST ADJACENT THERETO ON THE SIDE THEREOF TOWARD THE OTHER DOUBLE CHAIN, A MOTOR SUPPORT PIVOTED ON THE FRAME BETWEEN THE WHEELS FOR MOVEMENT ABOUT AN AXIS PARALLEL TO THE WHEEL AXIS, A DRIVE MOTOR ON THE MOTOR SUPPORT HAVING A DOUBLE ENDED DRIVE SHAFT, A RELATIVELY SMALL DRIVE SPROCKET ON EACH END OF THE DRIVE SHAFT POSITIONED RESPECTIVELY WITHIN THE PERIPHERIES OF SAID SECOND STRANDS AND ENGAGEABLE THEREWITH, MEANS FOR PIVOTING THE MOTOR SUPPORT TO MESH THE DRIVE SPROCKETS WITH THE SECOND STRANDS TO DRIVE THE WHEELS SYNCHRONOUSLY OR TO DISENGAGE THE DRIVE SPROCKETS FROM THE SECOND STRANDS TO PERMIT INDEPENDENT DIFFERENTIAL MOVEMENT OF THE WHEELS, AND MEANS FOR COUPLING THE FRAME TO A FOLDING BLEACHER. 